Add try catch to unguarded JSON.parse

[jcubic]

Information:

• Prism version: [e.g. 1.14, latest from the download page, etc.]: latest
• Plugins: [a list of plugins you are using or 'none']: none
• Environment: [e.g. Browser, Node, Webpack]: browser

Description
Inside the code, there is this snippet:

if (!_.disableWorkerMessageHandler) {
	// In worker
	_self.addEventListener('message', function (evt) {
		var message = JSON.parse(evt.data);
		var lang = message.language;
		var code = message.code;
		var immediateClose = message.immediateClose;
        
		_self.postMessage(_.highlight(code, _.languages[lang], lang));
		if (immediateClose) {
			_self.close();
		}
	}, false);
}

And it interferes with other code that don't send JSON data. We can add try catch that is ignored?
Probably my Chrome extensions.

Adding this:

window.Prism = window.Prism || {};
Prism.disableWorkerMessageHandler = true;

Makes no difference, I keep getting JSON parse error in console when including Prism.js.

I can create a PR.